A modern acoustical stethoscope typically has a head having a microphone containing a diaphragm. Some stethoscopes combine in the head both a diaphragm microphone and a bell microphone.
The acoustical stethoscope is used to diagnose the condition of a patient based on the acoustical output from the body of the patient. The frequency of the body's acoustical output is in the very low range of normal human hearing and less than the 3,000 Hertz (Hz) frequency where humans perceive sounds most strongly.
For example, the acoustic output from the heart has a spectrum from about the threshold of hearing to about 175 Hz corresponding to the normal opening and closing of the heart valves. Diagnosis of pathological conditions such as murmurs or clicks occurs in the acoustical spectrum from the heart of from about 200 Hz to about 350 Hz, with occasional pathological states presenting acoustic energy in somewhat higher ranges, e.g. to about 650 Hz.
Unfortunately, the threshold of audibility of a sound at a given frequency varies widely in the presence of other sounds from which it must be discriminated. Often, a sound of a lower frequency through its acoustic overtones can mask a sound of a higher frequency. Masking of the pathological heart sounds in the region of 200-350 Hz by the normal heart sounds at lower frequencies has been reduced by providing a diaphragm in the microphone of a stethoscope which attenuates the low frequency, normal heart sounds while transmitting the higher frequency, pathological condition sounds.
The diaphragm microphone of stethoscope heads has been constructed to overcome the effects of masking by providing a head which permits the diaphragm to move among several positions, such as that disclosed in U.S. Pat. No. 3,223,195; a diaphragm which floats in the microphone, such as that disclosed in U.S. Pat. No. 4,475,619; and a diaphragm against which pressure is applied to tune acoustical reception, such as that disclosed in U.S. Pat. No. 4,440,258.
While such diaphragm microphone constructions seek to provide refined or tuned acoustical transmission of the condition of a patient, some patients are difficult to diagnose because the surface area of the skin where the stethoscope head is placed does not provide continuous contact for the surface area of the diaphragm. Neonatal, pediatric, and emaciated patients are examples of such patients.
Incomplete contact between the diaphragm microphone and the surface of the skin can result in extraneous noise in those frequencies where the acoustical output of pathological conditions may be found. Reducing the sound leakage on the open bell microphone of a stethoscope head is known, such as that disclosed in U.S. Pat. No. 4,502,562. But a diaphragm microphone has a larger surface area typically than an open bell microphone and the sound receiving surface area of the diaphragm must remain flexible for proper acoustical receipt of the acoustical output of the body of the patient. Generally, it has been believed that a diaphragm microphone constructed to receive certain frequencies while relatively attenuating others did not need any further adjustment to its acoustical performance.
However, what is needed in the art is a structure to adapt the diaphragm microphone of a head to reduce the effects of loss of surface contact with the patient without affecting the ability of the diaphragm to receive the acoustical output from the body of the patient at the critical frequencies necessary for diagnosis.